1. Field of the Invention
This invention relates to a method for the recovery of a polymerization inhibitor and more particularly to a method for the recovery of a phenolic polymerization inhibitor from a styrene distillation residue.
2. Description of the Prior Art
In the refinement by distillation of a material containing a vinyl aromatic compound such as styrene or vinyl styrene, there is followed the practice of adding to the material a phenolic polymerization inhibitor for the purpose of precluding the material from undergoing polymerization during the course of distillation. In such case, the polymerization inhibitor accumulates in the distillation residue (hereinafter referred to as "styrene tar"). Studies devoted to the development of a technique for the recovery of the phenolic polymerization inhibitor accumulated in the styrene tar have been under way for a fairly long time to date. U.S. Pat. Nos. 3,969,395 and 4,033,829, for example, disclose a method which comprises extracting the inhibitor from a styrene tar containing dinitrophenol polymerization inhibitor with an alkaline aqueous solution, then mixing the aqueous phase of the extract with a mineral acid and an organic solvent, recovering from the resultant mixture the organic phase containing the dinitrophenol polymerization inhibitor, and reusing the organic phase as the polymerization inhibitor.
Because the above technique requires the use of an alkaline aqueous solution and a mineral acid, the operation of this technique necessitates an apparatus resistant to acids and alkalis. Further, since the above-described recovery method involves chemical reactions, it is complicated to operate.
An object of this invention, therefore, is to provide a novel method for the recovery of a polymerization inhibitor.
Another object of this invention is to provide a novel method for recovering a phenolic polymerization inhibitor from a styrene distillation residue without requiring use of any acid or alkali.